The soldiers who died when an Army truck overturned in floodwaters at Fort Hood hailed from different states and had different levels of experience. But most of them shared at least one thing in common, according to details released by officials over the weekend: They were motor transport operators, tasked with driving troops and cargo on bases and battlefields. Staff Sgt. Miguel Angel Colonvazquez; Specialists Yingming Sun and Christine Faith Armstrong; Pvts. First Class Brandon Austin Banner and Zachery Nathaniel Fuller; Pvts. Isaac Lee Deleon, Eddy Raelaurin Gates and Tysheena Lynette James; and Cadet Mitchell Alexander Winey were all killed in last week’s accident in Texas, the army said. The soldiers were on a training mission when their vehicle got stuck in flooded Owl Creek in a remote section of the post Thursday. Troops in a following vehicle were able to rescue three of their comrades from the floodwaters, Maj. Gen. John Uberti told reporters. Even as authorities released more details about those who died, a key question remained unanswered: What caused the tragedy? “The circumstances of the accident are unknown at this time, pending an investigation,” military officials said Saturday. Carter: Investigation promised U.S. Defense Secretary Ash Carter, speaking at a press conference in Singapore, vowed to get answers. “As always, we’ll get to the bottom of this incident and others that occurred this week.” Christopher Haug, spokesman for the post, said the troops were learning to operate the Light Medium Tactical Vehicle (LMTV) and were not sent out in conditions too dangerous for training. “It was a situation where the rain had come and the water was rising quickly,” he said. “They regularly pass through these weather conditions like this. This was a tactical vehicle, and at the time they were in proper place. Just an unfortunate accident that occurred quickly.” Owl Creek regularly experiences flash floods, said Michael Harmon, emergency management coordinator for Bell County. ‘Routine’ training mission Haug declined to go into detail about the training mission except to describe it as “routine.” Retired Col. Robert Morgan, however, told CNN affiliate KXXV-TV that the LMTV may not operate well in high waters. The truck, which is used to transport troops and cargo, sits from 6 to 8 feet off the ground. Severe storms have pummeled Texas, leading to a record rainfall total in May. Gov. Greg Abbott has declared a state of disaster across 31 counties as more rain is expected. CNN meteorologist Chad Myers warned that saturated ground and swollen creeks, bayous and rivers cannot absorb the downpour. Record rainfall With 7.51 inches of rain in the first two days of June, Houston has surpassed its monthly average rainfall for the month – 5.9 inches. Fort Bend County, near Houston, is experiencing flooding it called “unprecedented,” its Office of Emergency Management said. Judge Bob Hebert said there have been more than 558 rescues and at least 1,400 homes affected by the water. He noted the Brazos River was at nearly 55 feet under the Richmond Bridge – 4 feet above the previous record set in 1994. “That is a lot of water,” he said. He warned residents to be prepared for quickly rising waters and evacuate even if water had not yet entered their homes. Mosquitoes also a threat Myers also warned the aftermath of the flooding would bring a different threat: mosquitoes. Stagnant water will likely not recede for weeks, and the insects were already buzzing. “This will last for weeks. I don’t have to tell you what that means for West Nile, for Zika,” Myers said, referring to two viruses spread to humans by mosquitoes. 500-year floods It’s the second year in a row that Texas has been hit by 500-year floods – an extreme event with odds of it happening only once every 500 years Meteorologists and other experts point toward climate change or the weather pattern El Niño as potential culprits. “It could just be really bad luck,” said CNN senior meteorologist Brandon Miller. “It just so happens that parts of Texas have seen them now in back-to-back years, and maybe even twice this year.” Climate change is a possible culprit because one of the expected effects from a warmer climate is heavier rainfall, prompting more flooding, such as that in South Carolina last year, Miller said. But scientists have had mixed results in attributing the flooding to climate change, he said.